1. Field of the Invention
The present invention relates to a hemispheric bearing apparatus, and more particularly, to a hemispheric bearing apparatus for preventing deformation of a hemisphere occurring when a shaft is push-fitted into a shaft inserting hole formed at the center of a hemisphere in a hemispheric bearing which supports a thrust load and a radial load at the same time.
2. Description of the Related Art
Recently, with improvement of technologies in computer industries, in retrieving data, storing them, and reproducing them, there has been a trend to require high accuracy in having no movement or oscillation of a shaft, as well as excellent rotation performance at high speed in driving motors, which are required of various machines, such as a polygon mirror driving gear of a laser printer, a spindle motor of a hard disk, a head driving motor of a VCR, and the like. In this respect, a driving motor capable of stably rotating at high speed by reducing movement or oscillation of the shaft has been developed together with various kinetic pressure fluid bearing apparatuses which enable the shaft of the driving motor to rotate.
In such kinetic pressure fluid bearing apparatuses, there are provided a kinetic pressure generating groove which supports a shaft direction load, and another kinetic pressure generating groove which supports a radial load against the shaft direction. However, in a hemispheric bearing apparatus which has recently been developed, there is provided one kinetic pressure generating groove which supports the shaft direction load and the radial load.
A conventional hemispheric bearing apparatus will be described below.
In the conventional hemispheric bearing apparatus, a pair of hemispheres whose surfaces face each other are tightly fitted into a fixing shaft. A spiral shaped kinetic pressure generating groove having a predetermined depth is formed on the surfaces of the pair of hemispheres. The hemispheres face a cylindrical shaped bushing in which the hemispheric surfaces are engraved. The bushing rotates without contacting with the hemispheres by a kinetic pressure generated by the kinetic pressure generating groove of the hemispheres.
At this time, to maintain a predetermined clearance of several .mu.m between the hemispheric surface and a hemispheric groove of the bushing which face each other, a spacer is precisely formed between the hemispheres. A motor is mounted on an external surface of the bushing. The hemispheric surface and the hemispheric groove of the bushing rotate without contacting each other by a fluid pressure generated by the kinetic pressure generating groove formed on the hemispheric surface as the motor rotates.
However, the aforementioned conventional hemispheric bearing apparatus has several problems.
If the position of the hemisphere fitted into the shaft 20 is varied (see FIG. 1), the clearance formed between the hemispheric surface and the hemispheric groove of the bushing 40 is varied, thereby significantly reducing bearing performance. For this reason, the hemisphere is tightly fitted into the shaft. In this case, deformation of the hemisphere having high accuracy (sphericity; 0.05 .mu.m) occurs due to inner stress occurring when the hemisphere is tightly fitted into the shaft because the shaft hole formed in the hemisphere has a diameter smaller than that of the shaft. As illustrated in FIG. 1, the hemisphere surfaces 30c and 30d are deformed so that the clearances between the hemispheres 30 and 35 and the hemispheric grooves 30a and 30b becomes uneven. The fluid pressure is unevenly distributed between the hemispheres and the hemispheric grooves, resulting in deterioration of rotative performance. In addition, the hemispheres are partially contacted with the hemispheric surfaces to cause abrasion of the hemispheres, thereby reducing life-span of the hemispheric bearing.